Technical Field
The present invention relates to compositions for forming a top coat layer that are used in a photolithography method. To be more specific, the invention relates to a composition for forming a top coat layer that is formed on a resist layer prior to exposure of the resist layer for extreme ultraviolet rays in cases where an attempt to form resist patterns is made by the photolithography method. Further, the present invention relates to a pattern formation method using such composition for forming a top coat layer.
Background Art
As the size of various devices is becoming smaller, higher integration of semiconductor integrated circuits are demanded these days. In order to response to that, finer resist patterns have been demanded as well. In order to meet such needs, it is necessary to exposure using light with a shorter wavelength in the photolithography method. Thus, the light employed has become one with a shorter wavelength. As a result, visible light to ultraviolet rays and far ultraviolet rays can be used. Even extreme ultraviolet rays come to be used. Because ultrafine patterns are required to be formed in manufacturing process of semiconductor devices such as IC or LSI, to be more specific, DRAM, flash memory or logic-based semiconductor, photolithography by extreme ultraviolet rays is becoming more important.
In response to this, various resist compositions have been developed, which resist compositions have a sensitivity to light with different wavelengths. Here, it has been thought that almost all conventional commercially-available chemically amplified resists can be used in the photolithography method using extreme ultraviolet ray. Specifically, commonly-used resists for KrF laser exposure or resists for ArF laser exposure have been considered to be usable also in photolithography involving exposure to extreme ultraviolet rays. In practice, however, a large number of problems such as resolution, sensitivity, or roughness remain to be desirably improved in a current situation.
Meanwhile, there also remain problems in terms of a source of light and a mask in an exposure apparatus, which has caused delay in putting photolithography methods using extreme ultraviolet rays into practical use. Light with long wavelength contained in a source of extreme ultraviolet rays, in particular, deep ultraviolet light, for example, light with a wavelength 193 nm and 248 nm has been recognized as an important cause ascribed to deterioration of shape of resist patterns. As mentioned above, in cases where the resist composition for KrF laser or for ArF laser are employed in the photolithography method using extreme ultraviolet rays, it is obvious that these resists also exhibit a high sensitivity to deep ultraviolet rays.
Because of this, in cases where the pattern is formed by the photolithography method using extreme ultraviolet rays, a source of light with less content of such deep ultraviolet rays is desired. In order to remove the deep ultraviolet ray out of light irradiated from a exposure apparatus, a method of generating extreme ultraviolet rays is adjusted, for example, an optics system is adjusted. It is, however, difficult to completely remove the deep ultraviolet ray in a conventional source of exposure light; and it has been failed to keep the content of the deep ultraviolet ray contained in the extreme ultraviolet ray not more than 3% in a conventional exposure apparatus. As just described, the deep ultraviolet ray contained in extreme ultraviolet ray is a factor that causes deterioration of resist pattern roughness and deterioration of pattern shape; and a means to improve such problems has been sought.
Further, the exposure by extreme ultraviolet rays is in general carried out in high vacuum conditions. Because of this, upon the exposure in the photolithography method, each of the components of compositions such as photosensitive materials or photo acid generators that are contained in the resist layer, or low molecular weight compounds formed by a photoreaction often volatilize as gas. Such gas is referred to as outgas and may contaminate the optics system such as mirrors, photo masks, or the like in the exposure apparatus, resulting in deteriorated exposure accuracy. It has therefore been desired to inhibit the gas volatilizing for the resist as well.
For these problems, what has been develop is a method of forming a top coat layer on a resist layer, which top coat layer inhibits release of gas out of the resist layer and passes through extreme ultraviolet rays but absorbs deep ultraviolet light (Patent Document 1). Polymers that can be used for such a top coat layer and absorb deep ultraviolet rays have also been studied. That is, for the purpose of enhancing the top coat layer's effect of absorbing the deep ultraviolet ray, polymers having benzene, naphthalene or anthracene backbones were used (Patent Document 2). And, for the purpose of more enhancing the absorption of deep ultraviolet ray, studies have been conducted on search for polymer types and combination of polymers.